A

A paradox lies close to the heart of scientific discovery. If you know just what you are looking for, finding it can hardly count as a discovery, since it was fully anticipated. But if, on the other hand, you have no notion of what you are looking for, you cannot know when you have found it, and discovery, as such, is out of the question. In the philosophy of science, these extremes map onto the purest forms of deductivism and inductivism: In the former, the outcome is supposed to be logically contained in the premises you start with; in the latter, you are recommended to start with no expectations whatsoever and see what turns up.

B

As in so many things, the ideal position is widely supposed to reside somewhere in between these two impossible-to-realize extremes. You want to have a good enough idea of what you are looking for to be surprised when you find something else of value, and you want to be ignorant enough of your end point that you can entertain alternative outcomes. Scientific discovery should, therefore, have an accidental aspect, but not too much of one. Serendipity is a word that expresses a position something like that. It’s a fascinating word, and the late Robert King Merton—the father of the sociology of science’—liked it well enough to compose its biography, assisted by the French cultural historian Elinor Barber.

C

Serendipity means a “happy accident’ or ‘pleasant surprise’; specifically, the accident of finding something good or useful without looking for it. The first noted use of serendipity in the English language was by Horace Walpole (1717-1792). In a letter to Horace Mann (dated 28 January 1754) he said he formed it from the Persian fairy tale The Three Princes of Serendip, whose heroes ‘were always making discoveries, by accidents and sagacity, of things they were not in quest of’. The name stems from Serendip, an old name for Sri Lanka.

D

Besides antiquarians, the other community that came to dwell on serendipity to say something important about their practice was that of scientists. Many scientists, including the Harvard physiologist Walter Cannon and, later, the British immunologist Peter Medawar, liked to emphasize how much of scientific discovery was unplanned and even accidental. One of Cannon’s favorite examples of such serendipity is Luigi Galvani’s observation of the twitching of dissected frogs’ legs, hanging from a copper wire, when they accidentally touched an iron railing, leading to the discovery of ‘galvanismo; another is Hans Christian Orsted’s discovery of electromagnetism when he unintentionally brought a current-carrying wire parallel to a magnetic needle. The context in which scientific serendipity was most contested and had its greatest resonance was that connected with the idea of planned science. The serendipitists were not all inhabitants of academic ivory towers. Two of the great early-20th-century American pioneers of industrial research-Willis Whitney and Irving Langmuir, both of General Electric—made much play of serendipity, in the course of arguing against overly rigid research planning.

E

Yet what Cannon and Medawar took as a benign method, other scientists found incendiary To say that science had a significant serendipitous aspect was taken by some as dangerous denigration. If scientific discovery were really accidental, then what was the special basis of expert authority?

F

In this connection, the aphorism of choice came from no less an authority on scientific discovery than Louis Pasteur: “Chance favors the prepared mind.” Accidents may happen, and things may turn up unplanned and unforeseen, as one is looking for something else, but the ability to notice such events, to see their potential bearing and meaning, to exploit their occurrence and make constructive use of them—these are the results of systematic mental preparation. What seems like an accident is just another form of expertise. On closer inspection, it is insisted, accident dissolves into sagacity

G

In 1936, as a very young man, Merton wrote a seminal essay on “The Unanticipated Consequences of Purposive Social Action.” It is, he argued, the nature of social action that what one intends is rarely what one gets: Intending to provide resources for buttressing Christian religion, the natural philosophers of the Scientific Revolution laid the groundwork for secularism people wanting to be alone with nature in Yosemite Valley wind up crowding one another. We just don’t know enough—and we can never know enough—to ensure that the past is an adequate guide to the future: Uncertainty about outcomes, even of our best-laid plans, is endemic. All social action, including that undertaken with the best evidence and formulated according to the most rational criteria, is uncertain in its consequences.